Expression of heterologous DNA sequences in a plant host is dependent upon the presence of operably linked regulatory elements that are functional within the plant host. Choice of the regulatory element will determine when and where within the organism the heterologous DNA sequence is expressed. Where continuous expression is desired throughout the cells of a plant, and/or throughout development, constitutive promoters are utilized. In contrast, where gene expression in response to a stimulus is desired, inducible promoters are the regulatory element of choice. Where expression in specific tissues or organs is desired, tissue-specific or tissue-preferred promoters may be used to drive expression preferentially in certain tissues or organs. Such tissue-specific or tissue-preferred promoters may be temporally constitutive or inducible. In either case, additional regulatory sequences upstream and/or downstream from a core promoter sequence may be included in expression constructs of transformation vectors to bring about varying levels of expression of heterologous nucleotide sequences in a transgenic plant.
As this field develops and more genes become accessible, a greater need exists for transformed plants with multiple genes, and these multiple exogenous genes typically need to be controlled by separate regulatory sequences. Further, some genes should be regulated constitutively, whereas other genes should be expressed at certain developmental stages or locations in the transgenic organism. Accordingly, a variety of regulatory sequences having diverse effects is needed.
Diverse regulatory sequences are also needed as undesirable biochemical interactions can result from using the same regulatory sequence to control more than one gene. For example, transformation with multiple copies of a regulatory element may cause problems, such that expression of one or more genes may be adversely affected.
Transgenic modulation of early sensing and signaling genes involved in abiotic stress responses requires expression of the transgenes early upon exposure to the stress and at a moderate level. Also, expression of such transgenes needs to be turned off at later stages of stress exposure so as to avoid the continued induction of downstream targets, a scenario which can easily lead to yield penalty. The current invention provides two regulatory sequences which can be used for early expression and tight modulation of signaling and sensing genes, for transgenic modulation of plant stress tolerance.
The inventors herein disclose the isolation and characterization of promoters associated with stress-related transcription factors that can serve as regulatory elements for expression of isolated nucleotide sequences of interest, thereby impacting various traits in plants. Alternatively or additionally, the promoters may be used to drive scorable markers.